The present invention relates generally to crystalline materials. More particularly, the present invention provides a seed crystal and method using back and front side deposition of crystalline materials, e.g., GaN, AlN, InN. In a specific embodiment, the seed crystals can be used in an ammonothermal growth process or the like. Merely by way of example, the present substrate materials can be used in applications such as such as light emitting diodes, integrated circuits, MEMS, medical devices, combination of these, among others.
Single-crystal gallium nitride (GaN) containing compounds and related alloy compounds containing aluminum and indium (AlN, AlxGa1-xN, InN, InxGa1-xN) are useful semiconducting materials. Such semiconductor materials can be useful for a variety of applications due to their large bandgap and high chemical and thermal stability. In recent years there has been significant technological advancement in electronic and optoelectronic devices based on these materials, such as transistors, solar cells, light-emitting diodes, and lasers, among others. Although some of these products are available in the commercial market today, lack of a suitable GaN substrate on which to grow these materials remains a limitation to both performance and providing low cost, volume production of devices.
Conventional approaches to growth of GaN, AlN or InN containing compounds (collectively referred to as “(Al,In)GaN” compounds) and devices employ foreign substrate materials (containing one or more primary chemical species which is different from Ga, Al, In, or N), a process known as “heteroepitaxy”. Heteroepitaxial approaches to growth of (Al,In)GaN containing compounds result in epitaxial films with high defect densities due to the large lattice mismatch, chemical dissimilarity and thermal expansion coefficient difference between the nitride materials and substrate. The presence of defects is well-known to be detrimental to device performance. The thermal expansion coefficient difference between the substrate and the epitaxial layer in heteroepitaxy results in strain gradients in the material which can lead to wafer curvature, referred to as bow or warp, after growth. As used herein, the terms bow and warp are used in a manner which is well understood in this art. Definitions, for example, can be found from SEMI (www.semi.org), but can be others commonly known. There is therefore a need for bulk GaN substrates of high crystalline quality, ideally cut from large volume bulk GaN ingots.
Ammonothermal growth is a promising low cost and potentially highly scalable approach to produce such a GaN ingot. Ammonothermal growth has provided high quality crystalline material. Unfortunately, drawbacks exist. As an example, ammonothermal growth techniques lead to small sized crystals, which are often not useful for commercial applications. Additionally, defects in the seed material used for ammonothermal growth often replicate on any grown crystal structures. These and other limitations often exist with conventional ammonothermal techniques.
From the above, it is seen that techniques for improving crystal growth are highly desired.